Photons and transparency....who's right?

  • Context: Graduate 
  • Thread starter Thread starter JFS321
  • Start date Start date
  • Tags Tags
    Photons
Click For Summary

Discussion Overview

The discussion revolves around the behavior of photons in transparent materials, particularly focusing on the mechanisms of interaction with electrons in such media. Participants explore various models and explanations, including quantum electrodynamics (QED) and classical electromagnetic wave theories, while addressing concepts of absorption, reflection, and transparency.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant notes conflicting explanations regarding whether photons are absorbed and re-emitted by electrons in transparent materials or if they pass through without interaction due to insufficient energy.
  • Another participant suggests that any interaction between a photon and an electron involves energy absorption, but questions whether this absorption is sufficient to cause an electron to jump energy levels.
  • A different viewpoint emphasizes the complexity of describing light in materials using photons, advocating for a classical approach with electromagnetic waves and Lorentz oscillators as more accessible.
  • One participant raises the question of whether there is a universally correct mental model for understanding photon behavior in transparent media.
  • Another participant clarifies that in a transparent medium like glass, electrons are bound too strongly to allow simple photon interactions, contrasting this with interactions involving free electrons, such as in the Compton effect.

Areas of Agreement / Disagreement

Participants express differing views on the nature of photon interactions with electrons in transparent materials, indicating that multiple competing models and interpretations exist. The discussion remains unresolved regarding the correct mental model for these interactions.

Contextual Notes

Participants acknowledge the limitations of their models, particularly in relation to the energy levels of electrons and the complexity of photon interactions in various media. There is an emphasis on the need for a more nuanced understanding that may not be fully captured by simpler models.

JFS321
Messages
75
Reaction score
6
All, I have read as much as I can find online regarding this topic and there are so many conflicting answers that it is insane.

First, many sources identify photons vibrating the electrons in a transparent material in such a way that the net effect is to pass the photons out the other end of the medium. In this case, it seems to me that photons are being absorbed and re-emitted by each electron on the way through. HOWEVER, other sources state that photons pass through the medium (such as glass) and are not affected because they do not have sufficient energy to be "absorbed" by the electron...in other words...no interaction occurs.

1. But, is it not correct to say that anytime a photon interacts with an electron that it DOES absorb the energy, but perhaps not enough to jump energy levels?

2. In the case of reflection, the electron would absorb enough energy to jump to a higher state, and then re-emit the photon again as light. Therefore, reflection also requires an absorption of energy first, too. Correct?

Thanks in advance.
 
Science news on Phys.org
It is horribly complicated to describe light in materials using photons. To do it right would require to treat the whole system in QED - quantum electrodynamics. If you want to understand what is going, a classical picture with electromagnetic waves and Lorentz oscillators is much more accessible.
 
So, is there even necessarily a correct mental model to have regarding the behavior of photons in a transparent medium?
 
Perhaps a more specific question. Is it correct to say that any time a photon interacts with an electron, it is absorbed? Or, can you ever think of a photon reflecting from an electron as billiard balls would?
 
A transparent medium like glass contains electrons that are bound more strongly than the photon energy. So you cannot describe this with just the interaction between a photon and a free electron. Only for free electrons you could do that: the Compton effect, conservation of energy and momentum, like billiard balls.
 
JFS321 said:
So, is there even necessarily a correct mental model to have regarding the behavior of photons in a transparent medium?

Please start with our FAQ

https://www.physicsforums.com/threads/do-photons-move-slower-in-a-solid-medium.511177/

Zz.
 
Last edited by a moderator:

Similar threads

Undergrad Stimulated Emission & Emitted photon direction
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Are these explanations for color/light-absorption correct?
  • · Replies 5 ·
Replies
5
Views
2K
Graduate Classically, how can I explain Reflection?
  • · Replies 4 ·
Replies
4
Views
2K
Graduate Light in a medium: do phonons store light energy?
  • · Replies 1 ·
Replies
1
Views
1K
High School How far do photons travel inside common lasers?
  • · Replies 6 ·
Replies
6
Views
2K
Graduate Few questions on light interacting with atoms
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Lower speed of light inside a transparent medium
  • · Replies 17 ·
Replies
17
Views
3K
Undergrad Photons passing through transparent material
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad What happens to 'unabsorbed' photons?
  • · Replies 3 ·
Replies
3
Views
5K
Graduate Thought experiments suggest problem with published work
  • · Replies 8 ·
Replies
8
Views
2K